Flooding in NE Australia: How Ongoing Monitoring of Flood Plumes Helps in Managing the Great Barrier Reef

In January, massive flooding in the Australian state of Queensland killed at least 35 people and sent plumes of muddy, polluted water downstream and into the Great Barrier Reef Marine Park. The marine park's water quality management program (www.gbrmpa.gov.au/corp_site/key_issues/water_quality) monitors a wide array of nutrients and pollutants that flow from the neighboring river catchments to the MPA's waters. The program includes a flood plume monitoring program directed by Michelle Devlin of James Cook University. Here Devlin describes the monitoring program and how it informs park management:

"There is a flood somewhere, every year, in the Great Barrier Reef region. The aim of our flood plume monitoring program is to understand the short-term impacts of the river plumes, where the plumes go, and what it means for the marine environment when they get there. From information on the movement, extent, and concentrations of flood plumes, we are able to map high exposure areas and start to identify areas at risk from particular pollutants, depending on adjacent catchment.

"Thus it allows a greater understanding of short-term impacts as well as areas that may be at higher risk from altered water quality. This information can be used spatially to identify and correlate with our understanding of the short- and long-term changes associated with biological communities. As we gain confidence that an impact is identified with a particular pollutant, for example, we can deliver that information to managers to address the problem.

"Monitoring of riverine plumes on the GBR has been carried out sporadically for several decades. However, recent concern on the impact of catchment activities on Great Barrier Reef water quality has led to a reinvigorated sampling program, where the monitoring and mapping of plume waters is an integral component of a multidisciplinary program, including ambient water quality measurements, monitoring of inshore corals and seagrasses, and herbicide detection.

"This year, we have had the onset of an early wet season (November in comparison to January) in the central Great Barrier Reef region, and high flow in the Fitzroy River from November, culminating in the major flow event in early January. There have also been record flows in rivers south of the Fitzroy (outside of the marine park boundary) in the Mary-Burnett and Brisbane Rivers in which plume waters have moved north and joined up with the Fitzroy plume. We still have another two months of the wet season to go.

"With the recent flooding event, the quality of the water is concerning with elevated concentrations of sediment, nutrients (particularly dissolved nitrogen), and pesticides. Plume waters are low-salinity waters; this can and does stress the corals and seagrasses. So the combination of low-salinity waters with high concentrations of pollutants can be quite a toxic mixture to the biological systems. Lower-salinity conditions can also decrease the temperature threshold at which corals are likely to bleach, so plume-impacted areas may be more susceptible to the higher summer temperatures.

"It is important to note that our research also looks into the long-term changes that are associated with changes in water quality. Oversupply of dissolved nitrogen, dissolved sediments, and pesticides has begun to change the baseline: on the reef, we are seeing longer periods of high turbidity in the dry season, as well as higher annual means of chlorophyll a. There is also concern that the frequency and size of the flow events is increasing, but there are no concrete data on that yet."

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